Blood circulates through vessels of the human body and these vessels have a surface adapted for this purpose, i.e., a nonthrombogenic surface. Platelets do not adhere to such nonthrombogenic surfaces and so there is no coagulation.
Extracorporeal circulation of blood for treatment purposes necessitates contact between the blood and an artificial surface. Thus, in dialysis the blood comes into contact with various hoses and the dialysis membrane. The same applies to plasmapheresis, or exposure of the blood to immobilized enzymes or other substances intended for purification.
When blood contacts an artificial surface, the coagulation system is activated, depositing blood platelets, leading to thromboses, which occur either locally in contact with the artificial surface, or more generally within the human body.
The materials used for the extracorporeal circulation and treatment of blood are selected for biocompatibility, and especially haemocompatibility. However, this is not always sufficient. Therefore, workers have attempted to improve such materials by means of various treatments.
Thus, Miyama describes a material formed by graft copolymerization of methoxypolyethylene glycol methacrylate and polyacrylonitrile thioamide. Miyama et al., Journal of Applied Polymer Science, "Graft Copolymerization of Methoxypoly(ethylene glycol) Methacrylate Onto Polyacrylonitrile and Evaluation of Nonthrombogenicity of the Copolymer", 35, 115-125 (1988). The authors disclosed an improvement in the nonthrombogenic character of the graft copolymer compared to the acrylonitrile polymer.
However, obtaining such a copolymer necessitates the use of a particular production process. Indeed, the techniques described by Miyama do not make it possible to improve, using relatively simple operations, the nonthrombogenic character of a support membrane without substantially modifying its nature.
It is advantageous to be able to preserve the nature, as well as the properties, of certain existing support membranes while at the same time improving their haemocompatibility.